1. Field of the Invention
The invention relates generally to a circuit configuration and method of manufacture of a low pass filter. More particularly, this invention relates to an improved circuit configuration and method of manufacture of a low pass filters with improved characteristics of pass band attenuation having increased filter slope achieved by distributed inductor-capacitor networks by implementing trenched transient voltage suppressor (TVS) technologies.
2. Description of the Relevant Art
The low pass filters are commonly applied for filtering out radio frequency signals from audio/video/data line signals. Typically, electro-magnetic interference (EMI) filtering and electrostatic discharge (ESD) protection are combined into a single chip by using the capacitance of the Zener diodes to implement the filter as shown in FIG. 1A. Furthermore, filters implemented by combining the resistor-capacitor (RC) and inductor-capacitor (LC) circuits, i.e., combined RC/LC filters, are integrated with the transient voltage suppressing (TVS) circuits as shown in FIG. 1B. The filters have a monolithic characteristic and have the advantages that the parasitic capacitances and inductances are reduced. Additionally, the for typical design of low pass filters to attenuate cellular band signals in the frequency range of 800 MHz to 3 GHz, the filtering performance is improved to achieve a signal attenuation of −25 to −35 dB.
Referring to FIG. 1C for illustrating the performance characteristics of a low pass filter. Typical low pass filter carries out a pass band attenuation by attenuating signals higher than a cutoff frequency fc. The attenuation of the pass band signals, i.e., signals with frequency lower than fc, to the stop band, i.e., signals with frequency higher than fc, has a definite slope that represents a gradual decrease of the signals in a range of frequencies around the cutoff frequency fc. The low pass filter typically has a roll off of signal transmission at high frequencies. In order to improve the filter performance, it is desirable to minimize the pass band attenuation with low series resistance. Implementation of LC (inductor-capacitor) type of low pass filter is more desirable than the RC (resistor-capacitor) type of low pass filters. Furthermore, it is desirable to increase the slope of the low pass filter. Theoretical analyses have demonstrated that distributed inductor-capacitor network instead of lumped LC filter has the advantage of generating a sharper attenuation with greater filter slope. Specifically, slope can be defined as:Slope=20n db/decadeWhere n is the number of poles of the distributed LC network as that implemented in the LC network. It is therefore desirable to configure a LC low pass filter with a distributed LC network with greater number of poles. However, a distributed LC network when implemented in the low pass filter can increase the size and further generate increase amount of parasitic capacitances, inductances and resistances. Conventional method of configuring and manufacturing a LC network low pass filter is therefore not able to take advantage of the distributed LC network to improve the filter performance.
Therefore, a need still exists in the fields of circuit design and device manufactures for providing a new and improved circuit configuration and manufacturing method to resolve the above-discussed difficulties. Specifically, a need still exists to provide new and improved low pass filter circuits that can minimize the pass band attenuation with low series resistance while increasing the filter slope. The new and improved low pass filter with increased number of poles by implementing the distribute LC network circuit must also be configurable and can be conveniently manufactured as integrated circuits of compact size and reduced parasitic effects due to the distributed LC network circuits such that the above discussed difficulties and limitations can be resolved.